f the universal habit of
borrowing. On the other hand, if one chemical laboratory should
discover a high explosive which may be used in blasting rock for making
the foundations for buildings, a nation might borrow the idea and use
it in warfare for the destruction of man.

Mr. Clark Wissler has shown in his book on _Man and Culture_ that there
are culture areas originating from culture centres. From these culture
centres the bow-and-arrow is used over a wide area. The domestication
of the horse, which occurred in central Asia, has spread over the whole
world. So stone implements of culture centres have been borrowed and
exchanged more or less throughout the world. The theory is that one
tribe or race invented one thing because of the {27} adaptability to
good environment. The dominant necessity of a race stimulated man's
inventive power, while another tribe would invent or discover some
other new thing for similar reasons. But once created, not only could
the products be swapped or traded, but, where this was impossible,
ideas could be borrowed and adapted through imitation.

However, one should be careful not to make too hasty generalizations
regarding the similar products in different parts of the world, for
there is such universality of the traits of the human mind that, with
similar stages of advancement and similar environments, man's adaptive
power would cause him to do the same thing in very much the same way.
Thus, it is possible for two races that have had no contact for a
hundred thousand years to develop indigenous products of art which are
very similar. To illustrate from a point of contact nearer home, it is
possible for a person living in Wisconsin and one in Massachusetts,
having the same general environment--physical, educational, ethnic,
religious--and having the same general traits of mind, through
disconnected lines of differentiation, to write two books very much
alike or two magazine articles very much alike. In the question of
fundamental human traits subject to the same environmental stimuli, in
a general way we expect similar results.

With all this differentiation, progress as a whole represents a
continuous change from primitive conditions to the present complex
life, even though its line of travel leads it through the byways of
differentiation. Just as the development of races has been through the
process of differentiation from an early parent stock, cultural changes
have followe